Adjustable spark gap



April 3, 1956 J. E. JENNINGS 2,740,915

ADJUSTABLE SPARK GAP Filed on. 18, 1954 //V \/E N TOP 5 J0 fMMETT JENN/NGS his ATTORNE Y United States Patent ADJUSTABLE SPARK GAP Jo Emmett Jennings, San Jose, Calif., assignor to Jennings Radio Manufacturing Corporation, San Jose, Calif., a corporation of California 7 Application October 18, 1954, Serial No. 462,665

2 Claims. (Cl. 313-148) My invention relates to spark gaps and the principal object of the invention is the provision of a spark gap within a vacuumized envelope, and which is adjustable for operation over a wide range of frequencies, voltage and current.

Another object is the provision of a spark gap of the character described which is adjustable between the points to compensate for loss of the vaporized metal.

Another object is the provision of a vacuumized spark gap in which discharge in operation does not build up a metallic deposit on the inside of the envelope to cause electron focusing with consequent puncture of the envelope and failure of the implement.

Another object is the provision of a spark gap capable of absorbing high transient voltages not infrequently superimposed on the radio frequency or direct current potentials of a tube during its operation.

Another object is the provision of a vacuumized spark gap in which costs of production and therefore sales price to the industry are lessened by simplicity of design and the use of duplicate parts.

Another object is the provision of a spark gap in a vacuumized envelope, embodying a thermally conductive structure which rapidly conducts heat incident to operation to large exterior radiating surfaces.

These and other objects of the invention will be made clear in the following description of the invention. I do not limit myself to the showing made by the description and drawing, but may adopt variant forms of the invention within the scope of the appended claims.

Electric circuits operated at either sustained or peaked high potential values require spark gaps as protection for the electrical equipment. In high power installations such as transmission lines for power companies, where the lines may be subject to lightning discharges, means for dissipating the enormously high and sudden potential acquired from the lightning discharge, without burning out expensive circuits and apparatus, is an urgent need.

This has been attempted by various means but none of them have been wholly successful over the entire or even a major part of the range of current and voltage to which the installations to be protected may be subjected. Some protective devices such as the high speed ignitron crow-bar overload protectors used with transmitters of 250,000 to 500,000 watts output are very expensive; and some, such as the commonly used ball gap, although of low cost, require interruption of the primary voltage before the arc is extinguished; and not infrequently may not operate at all due to an extremely rapid rise and decay time in the pulse of an unexpected high voltage.

It is the broad purpose of the present invention to supply a protective spark gap capable of supplying protection over the wide range thus indicated, and at relatively low cost; and I accomplish this by arranging tungsten points of empirically determined conformation and size within a vacuumized receptacle; and on a mounting means 2,740,915 Patented Apr. 3, 1956 capable of adjustment from outside the receptacle in order to vary the space between the points. The enclosing glass bulb or envelope is closed at each end with generally cylindrical copper seals, constituting external terminals for the internal points; and the shape of the glass bulb is important in preserving the operating efliciency and life of the device. Overall inductance is reduced by the use of relatively large diameter seals, which with the heavy mounting structure of the points are also a factor in the rapid dissemination of heat emanating from the discharge between the points.

Referring now to the drawings: Fig. l is a sectional view of my spark gap, the plane of section lying in the long axis of the envelope. For convenience this plane may be considered to be horizontal.

Fig. 2 is a diagrammatic view showing my spark gap in a circuit to be protected.

My spark gap comprises three main components.

(a) The vacuumized envelope formed of a glass bulb symmetrical about a longitudinal axis and closed at opposite ends by copper seal structures which also constitute the external terminals of the implement. The envelope is formed in two halves, in each of which are assembled parts of the complete device. The halves are joined together as the final step of assembly before evacuation of the envelope.

(b) The spark gap proper is formed by two internal tungsten points, and their mounting structures. One of the points and its supporting and related structure is disposed in each of the copper seals and are brought into cooperative relation by the union of the bulb halves; and

(0) External adjusting means for moving one of the point-mounting means relative to the other, and incorporated in one of the seal structures.

The glass bulb is formed of two like sections 2 and 3, in each of which one of the points and its related and mounting means is permanently assembled before the sections are fused together in the plane indicated by the line 4, and concentrically about the long axis 5. The envelope thus formed is vacuumized through the tubulation 6.

r The glass bulb portion 2 is closed on its small end by the copper seal 7 of generally cylindrical form and relatively largediameter as shown. The seal is connected to the glass by the well-known metal-to-glass joint 8; and in its cylindrical portion provides a socket seat in which is brazed a cylindrical-conoid mounting structure for the tungsten point 9.

This mounting comprises a copper cylindrical shell 10, tapered down at one end in a conical portion 11, which provides a secure seat for the tungsten point 9, held therein by high melting point solder. Preferably the cylindrical shell is closed at the tapered end by the base plate 12, rabbetted on the peripheral edge on both sides to facilitate the centering of the parts, which are then integrally united by brazing with high melting point solder. The tungsten point is shaped to continue the same conical surface as its mount; and terminates in a planar end surface 15 perpendicular to the long axis of the implement as shown. To prevent isolated pockets within the envelope during vacuumization one or more small holes 16 are formed in the cylindrical wall 10 of the mount and in the plate 12.

Within the bulb section 3, the movable or adjustable tungsten point 21 is arranged. The immediate support or mounting for the point is the same as that for the point 9, except that the base plate 22 closing the large end of the conical section 23 has on its outer face an inwardly extending recess forming a snug seat for the end 24 of the bellows 25. An aperture 26 in the plate 3 22 avoids formation of an isolated pocket within the point mount.

Mounted on the peripheral edge of the plate 22 by an inwardly extending flange 27 is the cylindrical copper shield 28 extending as shown well past the base of the conical portion 11 and spaced therefrom, so'that a shielding wall is interposed between the spaced points 9 and 21-, between which the spark occurs, and the envelope will to intercept electrons, vaporized metal, or other particles emanating from a discharge between the points. The shielding action is complete as to particles radiating in a straight line from the spark, but a minute and practically negligible portion will drift or bounce through the annular space between the rim 29 of the" shield and the cylinder 10.

The opposite end of the bellows, forming a s'leeve 30 is brazed to the inwardly turned flange 31 of the seal 32 which closes the small end of the bulb by means of the metal-to-glass joint 33.

Within the sleeve of the bellows and extending. well into the bellows is a bearing tube 34 brazed to the sleeve. This tube provides a journal slideway for the tube 35, threaded to the reenforcing ring36, brazed into the bellows end 24.

The outer end of the tube 35 carries a plug 37 held by screws .58, and in which the adjusting screw 39 is threaded. The adjusting screw is mounted in a thrust bearing 41 and provided with a knob 42 arranged in the cap 43. Turning the knob moves the point 21- in the line oi the axis toward or away from the point 9 to vary the spacing between them.

The blunt points concentrate the electrostatic'potential at a relatively small. spot; and because of theadjustable mounting of one of the points the spacing between them may be varied to compensate for loss of tungsten because of vaporization during discharge, or to condition the implement to control transients before valuable equipment is destroyed. Because of the shield 28 and the wide spacing of the bulb from the points no electron focusing with consequent failure of the bulb occurs.

Since the points are in vacuum, there is no corrosion,

oxidation or other contamination to deteriorate thethe construction shown, my implement will operate on the higher frequencies as well as on direct current and low frequencies. Because conductivity of heat is through the body of the conductor, and conductivity of an electrical charge is largely on the surface, the mounting structure I have provided for the tungsten points is characterized throughout by substantial surface areas and substantial cross sectional areas.

My spark gap is readily adjusted to spark over at 50,000 volts or more; and implements of the type described are currently in use with transmitters up to 500,000 watts output to protect vacuum tubes of 5000 watts or more from so-called flash arc of very high transient voltage.

In Fig. 2, my spark gap S is shown in the circuit C in parallel with load L. My spark gap is so adjusted that when the voltage in the circuit reaches a point endangering the equipment, my device functions to dissipate the" high potential until the line again drops to normal.

I claim:

I. An adjustable spark gap implementcomprising a' va'cuumized envelope having a glass bulb closed at opposite axial ends with copper seals constituting external terminals of the implement, one of said seals on the inside thereof forming a seat, a shell in the seat integrally united therewith and tapered to a fiat end extending into the envelope, a' second shell tapered to a flat end in spaced axial alig'nment with the first shell and end, a recessed head closing one end of the shell, a bellows integrally connected to the head and the other seal, and means inside the bellows for moving the head and connected shell to vary the spacing of the aligned flat ends.

2. A- spark gap implement comprising a pair of like conical shells in spaced axial alignment, each shell tapering to a fiat terminal surface lying at a right angle to the axis, a vacuumized envelope including a non-conductivebulb and aligned and oppositely disposed conductive endstructures constituting external terminals of the implement, conductive means integrally mounting within the envelope eachconical shell on its adjacent end structure, and a shield disposed about both conical shells to intercept emanations from the spark.

References Cited in the file of this patent UNITED STATES PATENTS 1 ,559,714 Lili'enfeld Nov. 3, 1925 2,491,971 H311 Dec. 20, 1949' 2,497,479 Vlach Feb. 14, -0 

